The objective of this research is to study the enzymes that synthesize lecithin in the human newborn lung. The alveoli of normal lungs are lined with a lipoprotein surfactant which contains significant quantities of lecithin. Lung extracts of human infants dying of respiratory distress syndrome with hyaline membranes have decreased lecithin and abnormal surface active properties. Lecithin is synthesized in mammalian tissue by two main pathways; (a) the CDP-choline pathway and (b) trimethylation of phosphatidyl ethanolamine. There has been little done to define the pathways of lecithin biosynthesis in human lung tissue. Specific goals are (1) to define optimum conditions for reliable assays for five enzymes of pulmonary lecithin biosynthesis in the human neonate, (2) to purify these enzymes several fold, (3) to study the relationships of these enzyme activities to such factors as gestational age, type of pulmonary disease (respiratory distress syndrome, bronchopulmonary dysplasia), familial respiratory distress, etc., (4) to make preliminary investigations on the control of pulmonary lecithin biosynthesis in human neonatal lung. Initial studies will be devoted to completing the standardization of the enzyme assays at maximal conditions. Several fold purification of the enzymes will be sought by the use of salt gradient precipitation and chromatography techniques. Enzyme activities of autopsy specimens will be analyzed to determine relationships between activity and other parameters, such as gestational age. The relative activities of the enzymes at maximal and similar conditions, kinetic constants and tissue substrate levels, and analysis of the action of lysolecithin on these biosynthetic enzymes will be undertaken to investigate the enzymatic control of pulmonary lecithin biosynthesis.